I remember having watched an american TV movie in which a young blond girl was studying classical music (opera). I don't remember her name, but she sang "Carmen Habanera". At the end of the song, she sang it with a modern version of Carmen (pop, hip hop or something like this).

Sounds like you might be looking for this:
Brave New Girl (TV Movie 2004) - IMDb (http://www.imdb.com/title/tt0403118/)